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<TITLE>Video Hook Documentation</TITLE>
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<H1>Video Hook Documentation</H1>
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<H1>Table of Contents</H1>
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<LI><A NAME="TOC1" HREF="hooks.html#SEC1">1. Introduction</A>
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<LI><A NAME="TOC2" HREF="hooks.html#SEC2">1.1 null.c</A>
<LI><A NAME="TOC3" HREF="hooks.html#SEC3">1.2 fish.c</A>
<LI><A NAME="TOC4" HREF="hooks.html#SEC4">1.3 imlib2.c</A>
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Video Hook Documentation




<H1><A NAME="SEC1" HREF="hooks.html#TOC1">1. Introduction</A></H1>

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The video hook functionality is designed (mostly) for live video. It allows
the video to be modified or examined between the decoder and the encoder.


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Any number of hook modules can be placed inline, and they are run in the
order that they were specified on the ffmpeg command line.


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Three modules are provided and are described below. They are all intended to
be used as a base for your own modules. 


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Modules are loaded using the -vhook option to ffmpeg. The value of this parameter
is a space seperated list of arguments. The first is the module name, and the rest
are passed as arguments to the Configure function of the module.




<H2><A NAME="SEC2" HREF="hooks.html#TOC2">1.1 null.c</A></H2>

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This does nothing. Actually it converts the input image to RGB24 and then converts
it back again. This is meant as a sample that you can use to test your setup.




<H2><A NAME="SEC3" HREF="hooks.html#TOC3">1.2 fish.c</A></H2>

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This implements a 'fish detector'. Essentially it converts the image into HSV
space and tests whether more than a certain percentage of the pixels fall into
a specific HSV cuboid. If so, then the image is saved into a file for processing
by other bits of code.


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Why use HSV? It turns out that HSV cuboids represent a more compact range of
colors than would an RGB cuboid.




<H2><A NAME="SEC4" HREF="hooks.html#TOC4">1.3 imlib2.c</A></H2>

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This allows a caption to be placed onto each frame. It supports inserting the
time and date. By using the imlib functions, it would be easy to add your own
graphical logo, add a frame/border, etc.


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